In a semiconductor device that uses a nitride semiconductor, a phenomenon called current collapse may occur in which the current decreases when a high electric field is applied. To avoid such a phenomenon, a field plate electrode structure is used to disperse the electric field in the element interior. On the other hand, the field plate electrode structure causes the parasitic capacitance to increase which may cause an increase of the switching loss. In such a semiconductor device using a nitride semiconductor, it is important to realize both the suppression of the current collapse and the reduction of the switching loss.